The Prime Minister's Child Poverty Reduction Bill has passed its third reading in Parliament with near unanimous support from political parties on both sides.

The bill, which will set measures and targets for reducing child poverty, inform strategy to achieve that and require transparent reporting on poverty levels and introduce accountability for governments, was a cornerstone of Labour's election campaign last year and on the list of achievements for the coalition Government's first 100 days in office.

The bill passed 119 votes in favour, with only Act opposed.

Speaking in Parliament today, Ardern said it was no longer just a Labour Party bill.

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"This is now an initiative that has been led by a coalition Government with the support of New Zealand First and the Green Party.

And it also is an initiative that has had the support of the National Party. I want to acknowledge that. This is this Parliament's collective challenge, and the groups that have come together in Parliament today to support it in this House mean that it will have an enduring legacy," Ardern said.

Ardern, who introduced the bill in January, has been invested in it for years before that. She referenced her maiden speech, made 10 years and two days ago.

"I don't often reflect on my maiden speech but it occurred to me, when thinking about my long-held desire to progress child poverty legislation, that it was in that speech that I first reflected on my motivations to be in here in Parliament," she said.

National agreed in October to support the bill to become law, with some amendments after Ardern and National leader Simon Bridges worked behind the scenes to come to an agreement.

National's social development spokeswoman Louise Upston said the legislation gave the Opposition and the public the opportunity to measure the progress of the Government.

"It's not just about incomes. It's got to be about improving health, improving education, improving our record on child abuse, as well as improving the number of households that rely on benefits," Upston said.

Minister for Children Tracey Martin said the Children's Commissioner, along with units inside the Department of the Prime Minister and Cabinet, Oranga Tamariki and other youth panels had made sure that the voices of children had been clearly articulated in the whole process.

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What tens of thousands of New Zealand children have said is the most important thing to them is time for you to spend with them. I know it sounds like a cliché but it truly can be that simple," Martin said.

Children's Commissioner Judge Andrew Becroft recently praised both National and Labour for supporting the bill.

"That was a game changer ... having a cross-party accord is historic and the bill is about to be passed any day now and it will be all systems go and I will be watching very closely," he said.

He said a key way to tackle child poverty would be to see benefits - which go to parents with children - increased annually, rather than the current sporadic nature of when a Government saw fit.